Re: [uml-devel] [PATCH] um: Switch clocksource to hrtimers

[Anton Ivanov <anton.ivanov@kot-begemot.co.uk>]

Same story.

Overall works quite well, the moment I give it the "dselect upgrade 
test" the userspace hangs.

Kernel continues to work - forwarding, icmp, uml_mconsole are fine.

A.

On 17/05/15 10:25, Thomas Meyer wrote:
> Switch the UML clocksource from interval timers to posix interval timers
> and move to a monotonic timer.
>
> This fixes suspend&resume related timer issues and improves network
> performance as TCP state machines are now fed with the correct time;
> also correct QoS and traffic shaping.
>
> Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
> ---
>
> diff --git a/arch/um/Makefile b/arch/um/Makefile
> index e4b1a96..43ef190 100644
> --- a/arch/um/Makefile
> +++ b/arch/um/Makefile
> @@ -130,7 +130,7 @@ export LDS_ELF_FORMAT := $(ELF_FORMAT)
>   # The wrappers will select whether using "malloc" or the kernel allocator.
>   LINK_WRAPS = -Wl,--wrap,malloc -Wl,--wrap,free -Wl,--wrap,calloc
>   
> -LD_FLAGS_CMDLINE = $(foreach opt,$(LDFLAGS),-Wl,$(opt))
> +LD_FLAGS_CMDLINE = $(foreach opt,$(LDFLAGS),-Wl,$(opt)) -lrt
>   
>   # Used by link-vmlinux.sh which has special support for um link
>   export CFLAGS_vmlinux := $(LINK-y) $(LINK_WRAPS) $(LD_FLAGS_CMDLINE)
> diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
> index 08eec0b..5949cae 100644
> --- a/arch/um/include/shared/os.h
> +++ b/arch/um/include/shared/os.h
> @@ -219,7 +219,7 @@ extern int set_umid(char *name);
>   extern char *get_umid(void);
>   
>   /* signal.c */
> -extern void timer_init(void);
> +extern void timer_set_signal_handler(void);
>   extern void set_sigstack(void *sig_stack, int size);
>   extern void remove_sigstack(void);
>   extern void set_handler(int sig);
> @@ -240,12 +240,16 @@ extern void um_early_printk(const char *s, unsigned int n);
>   extern void os_fix_helper_signals(void);
>   
>   /* time.c */
> -extern void idle_sleep(unsigned long long nsecs);
> -extern int set_interval(void);
> -extern int timer_one_shot(int ticks);
> -extern long long disable_timer(void);
> +extern void os_idle_sleep(unsigned long long nsecs);
> +extern int os_timer_create(void* timer);
> +extern int os_timer_set_interval(void* timer, void* its);
> +extern int os_timer_one_shot(int ticks);
> +extern long long os_timer_disable(void);
> +extern long os_timer_remain(void* timer);
>   extern void uml_idle_timer(void);
> +extern long long os_persistent_clock_emulation(void);
>   extern long long os_nsecs(void);
> +extern long long os_vnsecs(void);
>   
>   /* skas/mem.c */
>   extern long run_syscall_stub(struct mm_id * mm_idp,
> diff --git a/arch/um/include/shared/skas/stub-data.h b/arch/um/include/shared/skas/stub-data.h
> index f6ed92c..f98b9e2 100644
> --- a/arch/um/include/shared/skas/stub-data.h
> +++ b/arch/um/include/shared/skas/stub-data.h
> @@ -6,12 +6,12 @@
>   #ifndef __STUB_DATA_H
>   #define __STUB_DATA_H
>   
> -#include <sys/time.h>
> +#include <time.h>
>   
>   struct stub_data {
> -	long offset;
> +	unsigned long offset;
>   	int fd;
> -	struct itimerval timer;
> +	struct itimerspec timer;
>   	long err;
>   };
>   
> diff --git a/arch/um/include/shared/timer-internal.h b/arch/um/include/shared/timer-internal.h
> new file mode 100644
> index 0000000..03e6f21
> --- /dev/null
> +++ b/arch/um/include/shared/timer-internal.h
> @@ -0,0 +1,13 @@
> +/*
> + * Copyright (C) 2012 - 2014 Cisco Systems
> + * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
> + * Licensed under the GPL
> + */
> +
> +#ifndef __TIMER_INTERNAL_H__
> +#define __TIMER_INTERNAL_H__
> +
> +#define TIMER_MULTIPLIER 256
> +#define TIMER_MIN_DELTA  500
> +
> +#endif
> diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
> index f17bca8..d0bbd01 100644
> --- a/arch/um/kernel/process.c
> +++ b/arch/um/kernel/process.c
> @@ -27,6 +27,7 @@
>   #include <kern_util.h>
>   #include <os.h>
>   #include <skas.h>
> +#include <timer-internal.h>
>   
>   /*
>    * This is a per-cpu array.  A processor only modifies its entry and it only
> @@ -201,11 +202,8 @@ void initial_thread_cb(void (*proc)(void *), void *arg)
>   
>   void arch_cpu_idle(void)
>   {
> -	unsigned long long nsecs;
> -
>   	cpu_tasks[current_thread_info()->cpu].pid = os_getpid();
> -	nsecs = disable_timer();
> -	idle_sleep(nsecs);
> +	os_idle_sleep(UM_NSEC_PER_SEC / UM_HZ);
>   	local_irq_enable();
>   }
>   
> diff --git a/arch/um/kernel/skas/clone.c b/arch/um/kernel/skas/clone.c
> index 289771d..814ec8b 100644
> --- a/arch/um/kernel/skas/clone.c
> +++ b/arch/um/kernel/skas/clone.c
> @@ -24,6 +24,7 @@ void __attribute__ ((__section__ (".__syscall_stub")))
>   stub_clone_handler(void)
>   {
>   	struct stub_data *data = (struct stub_data *) STUB_DATA;
> +	timer_t timerid;
>   	long err;
>   
>   	err = stub_syscall2(__NR_clone, CLONE_PARENT | CLONE_FILES | SIGCHLD,
> @@ -35,8 +36,14 @@ stub_clone_handler(void)
>   	if (err)
>   		goto out;
>   
> -	err = stub_syscall3(__NR_setitimer, ITIMER_VIRTUAL,
> -			    (long) &data->timer, 0);
> +	/* create posix interval timer */
> +	err = stub_syscall3(__NR_timer_create, CLOCK_MONOTONIC, 0l, (long) &timerid);
> +	if (err)
> +		goto out;
> +
> +	/* set interval to the given value from copy_context_skas0() */
> +	err = stub_syscall4(__NR_timer_settime, (long) timerid, 0l,
> +						(long) &data->timer, 0l);
>   	if (err)
>   		goto out;
>   
> diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c
> index 117568d..d15966c 100644
> --- a/arch/um/kernel/time.c
> +++ b/arch/um/kernel/time.c
> @@ -1,4 +1,5 @@
>   /*
> + * Copyright (C) 2012-2014 Cisco Systems
>    * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
>    * Licensed under the GPL
>    */
> @@ -8,10 +9,12 @@
>   #include <linux/interrupt.h>
>   #include <linux/jiffies.h>
>   #include <linux/threads.h>
> +#include <linux/spinlock.h>
>   #include <asm/irq.h>
>   #include <asm/param.h>
>   #include <kern_util.h>
>   #include <os.h>
> +#include <timer-internal.h>
>   
>   void timer_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
>   {
> @@ -22,18 +25,20 @@ void timer_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
>   	local_irq_restore(flags);
>   }
>   
> -static void itimer_set_mode(enum clock_event_mode mode,
> +static void timer_set_mode(enum clock_event_mode mode,
>   			    struct clock_event_device *evt)
>   {
>   	switch (mode) {
>   	case CLOCK_EVT_MODE_PERIODIC:
> -		set_interval();
> +		os_timer_set_interval(NULL, NULL);
>   		break;
>   
> +	case CLOCK_EVT_MODE_ONESHOT:
> +		os_timer_one_shot(1);
> +
>   	case CLOCK_EVT_MODE_SHUTDOWN:
>   	case CLOCK_EVT_MODE_UNUSED:
> -	case CLOCK_EVT_MODE_ONESHOT:
> -		disable_timer();
> +		os_timer_disable();
>   		break;
>   
>   	case CLOCK_EVT_MODE_RESUME:
> @@ -41,68 +46,74 @@ static void itimer_set_mode(enum clock_event_mode mode,
>   	}
>   }
>   
> -static int itimer_next_event(unsigned long delta,
> +static int timer_next_event(unsigned long delta,
>   			     struct clock_event_device *evt)
>   {
> -	return timer_one_shot(delta + 1);
> +	return os_timer_one_shot(delta);
>   }
>   
> -static struct clock_event_device itimer_clockevent = {
> -	.name		= "itimer",
> +static struct clock_event_device timer_clockevent = {
> +	.name		= "posix-timer",
>   	.rating		= 250,
>   	.cpumask	= cpu_all_mask,
>   	.features	= CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
> -	.set_mode	= itimer_set_mode,
> -	.set_next_event = itimer_next_event,
> -	.shift		= 32,
> +	.set_mode	= timer_set_mode,
> +	.set_next_event = timer_next_event,
> +	.shift		= 0,
> +	.max_delta_ns	= 0xffffffff,
> +	.min_delta_ns	= TIMER_MIN_DELTA, //microsecond resolution should be enough for anyone, same as 640K RAM
>   	.irq		= 0,
> +	.mult		= 1,
>   };
>   
> -static irqreturn_t um_timer(int irq, void *dev)
> +static irqreturn_t um_timer_irq(int irq, void *dev)
>   {
> -	(*itimer_clockevent.event_handler)(&itimer_clockevent);
> +	(*timer_clockevent.event_handler)(&timer_clockevent);
>   
>   	return IRQ_HANDLED;
>   }
>   
> -static cycle_t itimer_read(struct clocksource *cs)
> +static cycle_t timer_read(struct clocksource *cs)
>   {
> -	return os_nsecs() / 1000;
> +	return os_nsecs() / TIMER_MULTIPLIER;
>   }
>   
> -static struct clocksource itimer_clocksource = {
> -	.name		= "itimer",
> +static struct clocksource timer_clocksource = {
> +	.name		= "timer",
>   	.rating		= 300,
> -	.read		= itimer_read,
> +	.read		= timer_read,
>   	.mask		= CLOCKSOURCE_MASK(64),
>   	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
>   };
>   
> -static void __init setup_itimer(void)
> +static void __init timer_setup(void)
>   {
>   	int err;
>   
> -	err = request_irq(TIMER_IRQ, um_timer, 0, "timer", NULL);
> -	if (err != 0)
> +	err = request_irq(TIMER_IRQ, um_timer_irq, IRQF_TIMER, "hr timer", NULL);
> +	if (err != 0) {
>   		printk(KERN_ERR "register_timer : request_irq failed - "
>   		       "errno = %d\n", -err);
> +		return;
> +    }
> +
> +    err = os_timer_create(NULL);
> +    if (err != 0) {
> +        printk(KERN_ERR "creation of timer failed - errno = %d\n", -err);
> +        return;
> +    }
>   
> -	itimer_clockevent.mult = div_sc(HZ, NSEC_PER_SEC, 32);
> -	itimer_clockevent.max_delta_ns =
> -		clockevent_delta2ns(60 * HZ, &itimer_clockevent);
> -	itimer_clockevent.min_delta_ns =
> -		clockevent_delta2ns(1, &itimer_clockevent);
> -	err = clocksource_register_hz(&itimer_clocksource, USEC_PER_SEC);
> +	err = clocksource_register_hz(&timer_clocksource, NSEC_PER_SEC/TIMER_MULTIPLIER);
>   	if (err) {
>   		printk(KERN_ERR "clocksource_register_hz returned %d\n", err);
>   		return;
>   	}
> -	clockevents_register_device(&itimer_clockevent);
> +	clockevents_register_device(&timer_clockevent);
>   }
>   
>   void read_persistent_clock(struct timespec *ts)
>   {
> -	long long nsecs = os_nsecs();
> +	long long nsecs = os_persistent_clock_emulation();
>   
>   	set_normalized_timespec(ts, nsecs / NSEC_PER_SEC,
>   				nsecs % NSEC_PER_SEC);
> @@ -110,6 +121,6 @@ void read_persistent_clock(struct timespec *ts)
>   
>   void __init time_init(void)
>   {
> -	timer_init();
> -	late_time_init = setup_itimer;
> +	timer_set_signal_handler();
> +	late_time_init = timer_setup;
>   }
> diff --git a/arch/um/os-Linux/internal.h b/arch/um/os-Linux/internal.h
> deleted file mode 100644
> index 0dc2c9f..0000000
> --- a/arch/um/os-Linux/internal.h
> +++ /dev/null
> @@ -1 +0,0 @@
> -void alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc);
> diff --git a/arch/um/os-Linux/main.c b/arch/um/os-Linux/main.c
> index df9191a..6e36f0f 100644
> --- a/arch/um/os-Linux/main.c
> +++ b/arch/um/os-Linux/main.c
> @@ -163,13 +163,13 @@ int __init main(int argc, char **argv, char **envp)
>   
>   	/*
>   	 * This signal stuff used to be in the reboot case.  However,
> -	 * sometimes a SIGVTALRM can come in when we're halting (reproducably
> +	 * sometimes a timer signal can come in when we're halting (reproducably
>   	 * when writing out gcov information, presumably because that takes
>   	 * some time) and cause a segfault.
>   	 */
>   
> -	/* stop timers and set SIGVTALRM to be ignored */
> -	disable_timer();
> +	/* stop timers and set timer signal to be ignored */
> +	os_timer_disable();
>   
>   	/* disable SIGIO for the fds and set SIGIO to be ignored */
>   	err = deactivate_all_fds();
> diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
> index 7b605e4..4a9be55 100644
> --- a/arch/um/os-Linux/signal.c
> +++ b/arch/um/os-Linux/signal.c
> @@ -13,7 +13,6 @@
>   #include <kern_util.h>
>   #include <os.h>
>   #include <sysdep/mcontext.h>
> -#include "internal.h"
>   
>   void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *) = {
>   	[SIGTRAP]	= relay_signal,
> @@ -23,7 +22,8 @@ void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *) = {
>   	[SIGBUS]	= bus_handler,
>   	[SIGSEGV]	= segv_handler,
>   	[SIGIO]		= sigio_handler,
> -	[SIGVTALRM]	= timer_handler };
> +	[SIGALRM]	= timer_handler
> +};
>   
>   static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
>   {
> @@ -38,7 +38,7 @@ static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
>   	}
>   
>   	/* enable signals if sig isn't IRQ signal */
> -	if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGVTALRM))
> +	if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGALRM))
>   		unblock_signals();
>   
>   	(*sig_info[sig])(sig, si, &r);
> @@ -55,8 +55,8 @@ static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
>   #define SIGIO_BIT 0
>   #define SIGIO_MASK (1 << SIGIO_BIT)
>   
> -#define SIGVTALRM_BIT 1
> -#define SIGVTALRM_MASK (1 << SIGVTALRM_BIT)
> +#define SIGALRM_BIT 1
> +#define SIGALRM_MASK (1 << SIGALRM_BIT)
>   
>   static int signals_enabled;
>   static unsigned int signals_pending;
> @@ -78,46 +78,47 @@ void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
>   	set_signals(enabled);
>   }
>   
> -static void real_alarm_handler(mcontext_t *mc)
> +static void timer_real_alarm_handler(mcontext_t *mc)
>   {
>   	struct uml_pt_regs regs;
>   
>   	if (mc != NULL)
>   		get_regs_from_mc(&regs, mc);
>   	regs.is_user = 0;
> -	unblock_signals();
> -	timer_handler(SIGVTALRM, NULL, &regs);
> +	timer_handler(SIGALRM, NULL, &regs);
>   }
>   
> -void alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
> +void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
>   {
>   	int enabled;
>   
>   	enabled = signals_enabled;
>   	if (!signals_enabled) {
> -		signals_pending |= SIGVTALRM_MASK;
> +		signals_pending |= SIGALRM_MASK;
>   		return;
>   	}
>   
>   	block_signals();
> -
> -	real_alarm_handler(mc);
> +	timer_real_alarm_handler(mc);
>   	set_signals(enabled);
>   }
>   
> -void timer_init(void)
> +void timer_set_signal_handler(void)
>   {
> -	set_handler(SIGVTALRM);
> +	set_handler(SIGALRM);
>   }
>   
>   void set_sigstack(void *sig_stack, int size)
>   {
> -	stack_t stack = ((stack_t) { .ss_flags	= 0,
> -				     .ss_sp	= (__ptr_t) sig_stack,
> -				     .ss_size 	= size - sizeof(void *) });
> +	stack_t stack = ((stack_t) {
> +	            .ss_flags = 0,
> +				.ss_sp    = (__ptr_t) sig_stack,
> +				.ss_size  = size - sizeof(void *)
> +	});
>   
> -	if (sigaltstack(&stack, NULL) != 0)
> +	if (sigaltstack(&stack, NULL) != 0) {
>   		panic("enabling signal stack failed, errno = %d\n", errno);
> +	}
>   }
>   
>   static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = {
> @@ -129,10 +130,9 @@ static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = {
>   
>   	[SIGIO] = sig_handler,
>   	[SIGWINCH] = sig_handler,
> -	[SIGVTALRM] = alarm_handler
> +	[SIGALRM] = timer_alarm_handler
>   };
>   
> -
>   static void hard_handler(int sig, siginfo_t *si, void *p)
>   {
>   	struct ucontext *uc = p;
> @@ -186,9 +186,9 @@ void set_handler(int sig)
>   
>   	/* block irq ones */
>   	sigemptyset(&action.sa_mask);
> -	sigaddset(&action.sa_mask, SIGVTALRM);
>   	sigaddset(&action.sa_mask, SIGIO);
>   	sigaddset(&action.sa_mask, SIGWINCH);
> +	sigaddset(&action.sa_mask, SIGALRM);
>   
>   	if (sig == SIGSEGV)
>   		flags |= SA_NODEFER;
> @@ -281,8 +281,8 @@ void unblock_signals(void)
>   		if (save_pending & SIGIO_MASK)
>   			sig_handler_common(SIGIO, NULL, NULL);
>   
> -		if (save_pending & SIGVTALRM_MASK)
> -			real_alarm_handler(NULL);
> +		if (save_pending & SIGALRM_MASK)
> +			timer_real_alarm_handler(NULL);
>   	}
>   }
>   
> diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
> index 908579f..f669f9d 100644
> --- a/arch/um/os-Linux/skas/process.c
> +++ b/arch/um/os-Linux/skas/process.c
> @@ -47,7 +47,7 @@ static int ptrace_dump_regs(int pid)
>    * Signals that are OK to receive in the stub - we'll just continue it.
>    * SIGWINCH will happen when UML is inside a detached screen.
>    */
> -#define STUB_SIG_MASK ((1 << SIGVTALRM) | (1 << SIGWINCH))
> +#define STUB_SIG_MASK ((1 << SIGALRM) | (1 << SIGWINCH))
>   
>   /* Signals that the stub will finish with - anything else is an error */
>   #define STUB_DONE_MASK (1 << SIGTRAP)
> @@ -199,12 +199,23 @@ static int userspace_tramp(void *stack)
>   {
>   	void *addr;
>   	int err;
> +	timer_t timer;
> +
> +	struct stub_data *data = (struct stub_data *) stack;
>   
>   	ptrace(PTRACE_TRACEME, 0, 0, 0);
>   
>   	signal(SIGTERM, SIG_DFL);
>   	signal(SIGWINCH, SIG_IGN);
> -	err = set_interval();
> +
> +	err = os_timer_create(&timer);
> +	if (err) {
> +		printk(UM_KERN_ERR "userspace_tramp - creation of timer failed, "
> +		       "errno = %d\n", err);
> +		exit(1);
> +	}
> +
> +	err = os_timer_set_interval(&timer, &data->timer);
>   	if (err) {
>   		printk(UM_KERN_ERR "userspace_tramp - setting timer failed, "
>   		       "errno = %d\n", err);
> @@ -271,8 +282,9 @@ int userspace_pid[NR_CPUS];
>   int start_userspace(unsigned long stub_stack)
>   {
>   	void *stack;
> -	unsigned long sp;
> +	unsigned long sp, remain;
>   	int pid, status, n, flags, err;
> +	struct stub_data *data = (struct stub_data *) stub_stack;
>   
>   	stack = mmap(NULL, UM_KERN_PAGE_SIZE,
>   		     PROT_READ | PROT_WRITE | PROT_EXEC,
> @@ -292,6 +304,18 @@ int start_userspace(unsigned long stub_stack)
>   	else
>   		flags |= SIGCHLD;
>   
> +	remain = os_timer_remain(NULL);
> +	if (remain == 0)
> +		remain = UM_NSEC_PER_SEC / UM_HZ;
> +
> +	*data = ((struct stub_data) {
> +			.timer  = ((struct itimerspec)
> +				{ .it_value.tv_sec  = 0,
> +				  .it_value.tv_nsec = remain,
> +				  .it_interval.tv_sec  = 0,
> +				  .it_interval.tv_nsec = UM_NSEC_PER_SEC / UM_HZ })
> +	});
> +
>   	pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack);
>   	if (pid < 0) {
>   		err = -errno;
> @@ -308,7 +332,7 @@ int start_userspace(unsigned long stub_stack)
>   			       "errno = %d\n", errno);
>   			goto out_kill;
>   		}
> -	} while (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGVTALRM));
> +	} while (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGALRM));
>   
>   	if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP)) {
>   		err = -EINVAL;
> @@ -341,8 +365,6 @@ int start_userspace(unsigned long stub_stack)
>   
>   void userspace(struct uml_pt_regs *regs)
>   {
> -	struct itimerval timer;
> -	unsigned long long nsecs, now;
>   	int err, status, op, pid = userspace_pid[0];
>   	/* To prevent races if using_sysemu changes under us.*/
>   	int local_using_sysemu;
> @@ -351,13 +373,8 @@ void userspace(struct uml_pt_regs *regs)
>   	/* Handle any immediate reschedules or signals */
>   	interrupt_end();
>   
> -	if (getitimer(ITIMER_VIRTUAL, &timer))
> -		printk(UM_KERN_ERR "Failed to get itimer, errno = %d\n", errno);
> -	nsecs = timer.it_value.tv_sec * UM_NSEC_PER_SEC +
> -		timer.it_value.tv_usec * UM_NSEC_PER_USEC;
> -	nsecs += os_nsecs();
> -
>   	while (1) {
> +
>   		/*
>   		 * This can legitimately fail if the process loads a
>   		 * bogus value into a segment register.  It will
> @@ -428,19 +445,7 @@ void userspace(struct uml_pt_regs *regs)
>   			case SIGTRAP:
>   				relay_signal(SIGTRAP, (struct siginfo *)&si, regs);
>   				break;
> -			case SIGVTALRM:
> -				now = os_nsecs();
> -				if (now < nsecs)
> -					break;
> -				block_signals();
> -				(*sig_info[sig])(sig, (struct siginfo *)&si, regs);
> -				unblock_signals();
> -				nsecs = timer.it_value.tv_sec *
> -					UM_NSEC_PER_SEC +
> -					timer.it_value.tv_usec *
> -					UM_NSEC_PER_USEC;
> -				nsecs += os_nsecs();
> -				break;
> +			case SIGALRM:
>   			case SIGIO:
>   			case SIGILL:
>   			case SIGBUS:
> @@ -487,8 +492,8 @@ __initcall(init_thread_regs);
>   
>   int copy_context_skas0(unsigned long new_stack, int pid)
>   {
> -	struct timeval tv = { .tv_sec = 0, .tv_usec = UM_USEC_PER_SEC / UM_HZ };
>   	int err;
> +	unsigned long remain;
>   	unsigned long current_stack = current_stub_stack();
>   	struct stub_data *data = (struct stub_data *) current_stack;
>   	struct stub_data *child_data = (struct stub_data *) new_stack;
> @@ -499,11 +504,19 @@ int copy_context_skas0(unsigned long new_stack, int pid)
>   	 * prepare offset and fd of child's stack as argument for parent's
>   	 * and child's mmap2 calls
>   	 */
> -	*data = ((struct stub_data) { .offset	= MMAP_OFFSET(new_offset),
> -				      .fd	= new_fd,
> -				      .timer    = ((struct itimerval)
> -					           { .it_value = tv,
> -						     .it_interval = tv }) });
> +	remain = os_timer_remain(NULL);
> +	if (remain == 0)
> +		remain = UM_NSEC_PER_SEC / UM_HZ;
> +
> +	*data = ((struct stub_data) {
> +			.offset	= MMAP_OFFSET(new_offset),
> +			.fd     = new_fd,
> +			.timer  = ((struct itimerspec)
> +					     { .it_value.tv_sec  = 0,
> +					       .it_value.tv_nsec = remain,
> +					       .it_interval.tv_sec  = 0,
> +					       .it_interval.tv_nsec = UM_NSEC_PER_SEC / UM_HZ })
> +	});
>   
>   	err = ptrace_setregs(pid, thread_regs);
>   	if (err < 0) {
> diff --git a/arch/um/os-Linux/time.c b/arch/um/os-Linux/time.c
> index e9824d5..0e2bb7d 100644
> --- a/arch/um/os-Linux/time.c
> +++ b/arch/um/os-Linux/time.c
> @@ -1,4 +1,5 @@
>   /*
> + * Copyright (C) 2012-2014 Cisco Systems
>    * Copyright (C) 2000 - 2007 Jeff Dike (jdike{addtoit,linux.intel}.com)
>    * Licensed under the GPL
>    */
> @@ -10,177 +11,172 @@
>   #include <sys/time.h>
>   #include <kern_util.h>
>   #include <os.h>
> -#include "internal.h"
> +#include <string.h>
> +#include <timer-internal.h>
>   
> -int set_interval(void)
> -{
> -	int usec = UM_USEC_PER_SEC / UM_HZ;
> -	struct itimerval interval = ((struct itimerval) { { 0, usec },
> -							  { 0, usec } });
> -
> -	if (setitimer(ITIMER_VIRTUAL, &interval, NULL) == -1)
> -		return -errno;
> +static timer_t event_high_res_timer = 0;
>   
> -	return 0;
> +static inline long long timeval_to_ns(const struct timeval *tv)
> +{
> +	return ((long long) tv->tv_sec * UM_NSEC_PER_SEC) +
> +		tv->tv_usec * UM_NSEC_PER_USEC;
>   }
>   
> -int timer_one_shot(int ticks)
> +static inline long long timespec_to_ns(const struct timespec *ts)
>   {
> -	unsigned long usec = ticks * UM_USEC_PER_SEC / UM_HZ;
> -	unsigned long sec = usec / UM_USEC_PER_SEC;
> -	struct itimerval interval;
> -
> -	usec %= UM_USEC_PER_SEC;
> -	interval = ((struct itimerval) { { 0, 0 }, { sec, usec } });
> +	return ((long long) ts->tv_sec * UM_NSEC_PER_SEC) +
> +		ts->tv_nsec;
> +}
>   
> -	if (setitimer(ITIMER_VIRTUAL, &interval, NULL) == -1)
> -		return -errno;
> +long long os_persistent_clock_emulation (void) {
> +	struct timespec realtime_tp;
>   
> -	return 0;
> +	clock_gettime(CLOCK_REALTIME, &realtime_tp);
> +	return timespec_to_ns(&realtime_tp);
>   }
>   
>   /**
> - * timeval_to_ns - Convert timeval to nanoseconds
> - * @ts:		pointer to the timeval variable to be converted
> - *
> - * Returns the scalar nanosecond representation of the timeval
> - * parameter.
> - *
> - * Ripped from linux/time.h because it's a kernel header, and thus
> - * unusable from here.
> + * os_timer_create() - create an new posix (interval) timer
>    */
> -static inline long long timeval_to_ns(const struct timeval *tv)
> -{
> -	return ((long long) tv->tv_sec * UM_NSEC_PER_SEC) +
> -		tv->tv_usec * UM_NSEC_PER_USEC;
> +int os_timer_create(void* timer) {
> +
> +	timer_t* t = timer;
> +
> +	if(t == NULL) {
> +		t = &event_high_res_timer;
> +	}
> +
> +	if (timer_create(
> +		CLOCK_MONOTONIC,
> +		NULL,
> +		t) == -1) {
> +		return -1;
> +	}
> +	return 0;
>   }
>   
> -long long disable_timer(void)
> +int os_timer_set_interval(void* timer, void* i)
>   {
> -	struct itimerval time = ((struct itimerval) { { 0, 0 }, { 0, 0 } });
> -	long long remain, max = UM_NSEC_PER_SEC / UM_HZ;
> +	struct itimerspec its;
> +	unsigned long long nsec;
> +	timer_t* t = timer;
> +	struct itimerspec* its_in = i;
>   
> -	if (setitimer(ITIMER_VIRTUAL, &time, &time) < 0)
> -		printk(UM_KERN_ERR "disable_timer - setitimer failed, "
> -		       "errno = %d\n", errno);
> +	if(t == NULL) {
> +		t = &event_high_res_timer;
> +	}
>   
> -	remain = timeval_to_ns(&time.it_value);
> -	if (remain > max)
> -		remain = max;
> +	nsec = UM_NSEC_PER_SEC / UM_HZ;
>   
> -	return remain;
> -}
> +	if(its_in != NULL) {
> +		its.it_value.tv_sec = its_in->it_value.tv_sec;
> +		its.it_value.tv_nsec = its_in->it_value.tv_nsec;
> +	} else {
> +		its.it_value.tv_sec = 0;
> +		its.it_value.tv_nsec = nsec;
> +	}
>   
> -long long os_nsecs(void)
> -{
> -	struct timeval tv;
> +	its.it_interval.tv_sec = 0;
> +	its.it_interval.tv_nsec = nsec;
>   
> -	gettimeofday(&tv, NULL);
> -	return timeval_to_ns(&tv);
> -}
> +	if(timer_settime(*t, 0, &its, NULL) == -1) {
> +		return -errno;
> +	}
>   
> -#ifdef UML_CONFIG_NO_HZ_COMMON
> -static int after_sleep_interval(struct timespec *ts)
> -{
>   	return 0;
>   }
>   
> -static void deliver_alarm(void)
> +/**
> + * os_timer_remain() - returns the remaining nano seconds of the given interval
> + *                     timer
> + * Because this is the remaining time of an interval timer, which correspondends
> + * to HZ, this value can never be bigger than one second. Just
> + * the nanosecond part of the timer is returned.
> + * The returned time is relative to the start time of the interval timer.
> + * Return an negative value in an error case.
> + */
> +long os_timer_remain(void* timer)
>   {
> -	alarm_handler(SIGVTALRM, NULL, NULL);
> -}
> +	struct itimerspec its;
> +	timer_t* t = timer;
>   
> -static unsigned long long sleep_time(unsigned long long nsecs)
> -{
> -	return nsecs;
> -}
> +	if(t == NULL) {
> +		t = &event_high_res_timer;
> +	}
>   
> -#else
> -unsigned long long last_tick;
> -unsigned long long skew;
> +	if(timer_gettime(t, &its) == -1) {
> +		return -errno;
> +	}
> +
> +	return its.it_value.tv_nsec;
> +}
>   
> -static void deliver_alarm(void)
> +int os_timer_one_shot(int ticks)
>   {
> -	unsigned long long this_tick = os_nsecs();
> -	int one_tick = UM_NSEC_PER_SEC / UM_HZ;
> +	struct itimerspec its;
> +	unsigned long long nsec;
> +	unsigned long sec;
>   
> -	/* Protection against the host's time going backwards */
> -	if ((last_tick != 0) && (this_tick < last_tick))
> -		this_tick = last_tick;
> +    nsec = (ticks + 1);
> +    sec = nsec / UM_NSEC_PER_SEC;
> +	nsec = nsec % UM_NSEC_PER_SEC;
>   
> -	if (last_tick == 0)
> -		last_tick = this_tick - one_tick;
> +	its.it_value.tv_sec = nsec / UM_NSEC_PER_SEC;
> +	its.it_value.tv_nsec = nsec;
>   
> -	skew += this_tick - last_tick;
> +	its.it_interval.tv_sec = 0;
> +	its.it_interval.tv_nsec = 0; // we cheat here
>   
> -	while (skew >= one_tick) {
> -		alarm_handler(SIGVTALRM, NULL, NULL);
> -		skew -= one_tick;
> -	}
> -
> -	last_tick = this_tick;
> +	timer_settime(event_high_res_timer, 0, &its, NULL);
> +	return 0;
>   }
>   
> -static unsigned long long sleep_time(unsigned long long nsecs)
> +/**
> + * os_timer_disable() - disable the posix (interval) timer
> + * Returns the remaining interval timer time in nanoseconds
> + */
> +long long os_timer_disable(void)
>   {
> -	return nsecs > skew ? nsecs - skew : 0;
> +	struct itimerspec its;
> +
> +	memset(&its, 0, sizeof(struct itimerspec));
> +	timer_settime(event_high_res_timer, 0, &its, &its);
> +
> +	return its.it_value.tv_sec * UM_NSEC_PER_SEC + its.it_value.tv_nsec;
>   }
>   
> -static inline long long timespec_to_us(const struct timespec *ts)
> +long long os_vnsecs(void)
>   {
> -	return ((long long) ts->tv_sec * UM_USEC_PER_SEC) +
> -		ts->tv_nsec / UM_NSEC_PER_USEC;
> +	struct timespec ts;
> +
> +	clock_gettime(CLOCK_PROCESS_CPUTIME_ID,&ts);
> +	return timespec_to_ns(&ts);
>   }
>   
> -static int after_sleep_interval(struct timespec *ts)
> +long long os_nsecs(void)
>   {
> -	int usec = UM_USEC_PER_SEC / UM_HZ;
> -	long long start_usecs = timespec_to_us(ts);
> -	struct timeval tv;
> -	struct itimerval interval;
> -
> -	/*
> -	 * It seems that rounding can increase the value returned from
> -	 * setitimer to larger than the one passed in.  Over time,
> -	 * this will cause the remaining time to be greater than the
> -	 * tick interval.  If this happens, then just reduce the first
> -	 * tick to the interval value.
> -	 */
> -	if (start_usecs > usec)
> -		start_usecs = usec;
> -
> -	start_usecs -= skew / UM_NSEC_PER_USEC;
> -	if (start_usecs < 0)
> -		start_usecs = 0;
> -
> -	tv = ((struct timeval) { .tv_sec  = start_usecs / UM_USEC_PER_SEC,
> -				 .tv_usec = start_usecs % UM_USEC_PER_SEC });
> -	interval = ((struct itimerval) { { 0, usec }, tv });
> -
> -	if (setitimer(ITIMER_VIRTUAL, &interval, NULL) == -1)
> -		return -errno;
> +	struct timespec ts;
>   
> -	return 0;
> +	clock_gettime(CLOCK_MONOTONIC,&ts);
> +	return timespec_to_ns(&ts);
>   }
> -#endif
>   
> -void idle_sleep(unsigned long long nsecs)
> +/**
> + * os_idle_sleep() - sleep for a given time of nsecs
> + * @nsecs: nanoseconds to sleep
> + */
> +void os_idle_sleep(unsigned long long nsecs)
>   {
>   	struct timespec ts;
>   
> -	/*
> -	 * nsecs can come in as zero, in which case, this starts a
> -	 * busy loop.  To prevent this, reset nsecs to the tick
> -	 * interval if it is zero.
> -	 */
> -	if (nsecs == 0)
> -		nsecs = UM_NSEC_PER_SEC / UM_HZ;
> -
> -	nsecs = sleep_time(nsecs);
> -	ts = ((struct timespec) { .tv_sec	= nsecs / UM_NSEC_PER_SEC,
> -				  .tv_nsec	= nsecs % UM_NSEC_PER_SEC });
> -
> -	if (nanosleep(&ts, &ts) == 0)
> -		deliver_alarm();
> -	after_sleep_interval(&ts);
> +	if (nsecs <= 0) {
> +		return;
> +	}
> +
> +	ts = ((struct timespec) {
> +			.tv_sec  = nsecs / UM_NSEC_PER_SEC,
> +			.tv_nsec = nsecs % UM_NSEC_PER_SEC
> +	});
> +
> +	clock_nanosleep(CLOCK_MONOTONIC, 0, &ts, NULL);
>   }
>
>
>
>
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